You could detonate cell phone IED’s using WIFI from another smart phone from that distance even if cell service was shut down.
As an Electrical Engineer (specializing in Telecommunications), you can detonate a device from a wide spectrum of frequencies.
The feds do not call the cell companies to shut down for a specific event...takes too long...Now in the long term, they will do this if they consider this a long term attack....example, not event specific but city wide...
They just “jam” the frequencies used 850MGZ to 1900MGZ and also the WIFI freq’s of 2.4 to 5.8....
A couple of well placed powerful freq jammers with control at a event security center could be implemented in seconds....This is really a low tech but effective solution...
I would imagine this is what happened based on the events that only two devices went off and the other two failed....
Of course, this would be an operational security issue so the feds would never admit to it, nor should they...